Optical fiber waveguides are being used with increasing regularity for the transmission and processing of optical signals. In addition to telecommunications applications, fiber optic sensors are used for measuring parameters such as temperature, pressure, radiation levels, chemical concentrations and the like. In an optical fiber sensor, for example, having a core and a surrounding cladding, the presence of chemical analytes can produce a change in the refractive indices of the cladding and core and consequently in the optical output of the fiber. A need exists, however, for improved optical fiber sensors that are more sensitive and that can produce greater variations in optical output.